1. Field of the Invention
The present invention relates to a lens barrel in which a linearly movable ring positioned inside a stationary barrel of the lens barrel moves linearly along an optical axis by a rotation of a hand-operated rotating ring positioned around the stationary barrel.
2. Description of the Related Art
As shown in FIGS. 4 and 5, a zoom lens (zoom lens barrel) having a zoom ring (hand-operated rotating ring) 50, a linear guide ring 30 and a first lens group moving ring (linearly movable ring) 51 which are coaxially arranged in this order radially from outside to inside the zoom lens is known in the art. A set of circumferential grooves 50a are formed on the zoom ring 50 while a corresponding set of rollers 70 which are fixed to the linear guide ring 30 are respectively engaged in the set of circumferential grooves 50a to restrict the movement of the zoom ring 50 relative to the linear guide ring 30. On the other hand, a set of cam engaging portions 56 projecting in the radial direction are formed integral with an inner peripheral surface of the zoom ring 50 to engage with a corresponding set of cam protrusions 51a of the first lens group moving ring 51, respectively, via the linear guide ring 30.
According to such structure of the conventional zoom lens, the linear guide ring 30 must be provided at the front end thereof with a set of cutout portions 58 to prevent the set of cam engaging portions 56 of the zoom ring 50 from interfering with the linear guide ring 30 when the linear guide ring 30 is installed in the zoom ring 50. Such cutout portions 58 deteriorate the strength of the linear guide ring 30. Moreover, the cutout portions 58 complicate the structure of the linear guide ring 30. This makes it difficult to form the linear guide ring by injection molding.
The present invention provides a lens barrel which includes a linear guide ring serving as a fundamental element of the lens barrel, and which has a structure making it possible to form the linear guide ring easily by injection molding with an increase in strength of the linear guide ring.
According to an aspect of the present invention, a lens barrel is provided, including a linear guide ring; a linearly movable ring which is provided inside the linear guide ring and has a cam on an outer circumferential surface; and a hand-operated rotating ring, provided outside the linear guide ring, which is capable of rotating in a circumferential direction and is incapable of rotating in an optical axis direction, with respect to the linear guide ring and which has a first penetrate groove. The linear guide ring, the linearly movable ring and the hand-operated rotating ring are provided concentrically to each other. A rotation motion of the hand-operated rotating ring with respect to the linear guide ring causes the linearly movable ring to move linearly along the optical axis direction, via the linear guide ring. The linear guide ring has a second penetrate groove penetrated in a radial direction. A projection member, which is to be engaged with the cam provided on the linear movable ring, via the second penetrate groove of the linear guide ring, is inserted from an outside of the hand-operated rotating ring.
When the projection member is inserted, a length of the projection member, which is positioned in the second penetrated groove, can be substantially the same as a length of the second penetrated groove, in the optical axis direction.
It is desirable for the second penetrated groove of the linear guide ring to be provided as a circumferential elongated groove in which the projection member does not block the rotation of the hand-operated rotating ring with respect to the linear guide ring.
It is desirable for the lens barrel to serve as a zoom lens so that a desired focal length can be set freely by moving the linearly movable ring relative to the linear guide ring by a rotation of the hand-operated rotating ring.
The linear guide ring can include at least one linear guide slot extending parallel to the optical axis, and the linearly movable ring can include at least one projection which is slidably engaged in the linear guide slot.
The linear guide ring can be a stationary ring.
The present disclosure relates to subject matter contained in Japanese Patent Application No.2002-280516 (filed on Sep. 26, 2002) which is expressly incorporated herein by reference in its entirety.